Plasminogen activation provides a general mechanism for producing pericellular proteolysis and it is a prominent component of many physiological and pathological processes. Despite its physiological and pharmacological importance, detailed biochemical and molecular information about plasminogen activation is sparse. The ultimate aim of this project is the acquisition of structural and biochemical data that might provide a basis for experimental design of small molecules capable of modulating the activity of several components of the fibrinolytic system, namely, plasminogen activators, plasminogen and plasmin. To this end, the following lines of work are proposed: (1) a structure-activity analysis of plasminogen activation, performed by engineering a range of variant plasminogen and assessing in detail their ability to serve as substrates for human urokinase, human tissue plasminogen activator, streptokinase, and, to a lesser extent, staphylokinase; (2) concurrent x-ray crystallographic analysis of a selected group of engineered plasminogen; of their streptokinase complexes; of the respective plasmin(s), and of their complexes with aprotinin (Kunitz inhibitor) (3) a detailed kinetic and equilibrium study of the plasminogen-streptokinase interaction.